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London Cylinder SpecialistAsk about your cylinder

Hot water cylinder specialists

Find the fault first. Then repair or replace the cylinder.

Unvented hot water cylinder, cutawayEngineering section through a mains-pressure unvented cylinder. Cold mains passes an inlet group (isolation, pressure reducing and check valves) with an expansion relief valve and expansion vessel, then enters the base of the cylinder. The temperature and pressure relief valve near the top and the expansion relief valve both discharge to a tundish with a visible air gap, then down an open discharge pipe that falls to a safe outlet. Inside are an immersion element, a heating coil fed through a 2-port motorised valve, a cylinder thermostat and a high-limit cut-out. Hot water leaves from the top, and heat is stratified, hottest at the top.Insulation jacket14Insulation jacketFoam, cut awayHot outlet8Hot outletTo taps and showersmains coldInlet group: isolation, pressure reducing and check valves1Inlet groupIsolate, reduce, checkExpansion relief valve2Expansion relief valveReleases pressureTemperature and pressure relief valve3TPRVHeat and pressureTundish with visible air gap4TundishVisible air gapDischarge pipe from the tundish, open to a safe outlet7Discharge pipeFalls to a safe outletExpansion vessel5Expansion vesselAbsorbs heated waterCold inlet at the base of the cylinder6Cold inletEnters at the baseDrain valveImmersion element9Immersion elementBackup, own cut-outCylinder thermostat10Cylinder thermostatSets the temperatureHigh-limit cut-out thermostat11High-limit cut-outManual reset2-port motorised valvefrom boiler122-port valveMotorised, boiler flowHeating coilto boiler13Heating coilBoiler heat exchangerUnvented cylinderSection, not to scalecoldhot

Or start from what you see

Fig. 1

Section through an unvented cylinder.

Select a part on the drawing, or start from a symptom, to see what it does, where it fails and what to read next.

London Cylinder Specialist diagnoses hot water cylinders across London. Diagnosis is a fixed £180, and what it finds decides the repair or the replacement.

Ask about your cylinderSee the fixed prices
Diagnosis
£180 fixed. There is no call-out fee.
Cover
London inside the M25, 24/7
Cylinder
Priced separately. It depends on type, size and your preference, and we recommend the right one.

Four checks, always in this order

A cylinder fault is rarely where it first shows. A fixed order means repair or replacement rests on what was found, not on a guess.

  1. Check 1

    Isolation and safety

    The heat sources and the water supply are isolated first. On an unvented cylinder the discharge pipework is checked for signs of steam or very hot water before anything is opened.

    Inlet group, Discharge pipe

  2. Check 2

    Stored temperature and controls

    The temperature of the stored water against the thermostat settings, the programmer and the motorised valves that tell the cylinder to heat.

    Cylinder thermostat, High-limit cut-out, 2-port valve

  3. Check 3

    Pressure and expansion devices

    On an unvented cylinder: the incoming pressure, the expansion vessel, the pressure and relief valves and the tundish.

    Expansion vessel, TPRV, Tundish

  4. Check 4

    Element, coil and valves

    The immersion element, the boiler coil feed and the valves that serve them, then the condition of the cylinder itself. That last check decides repair or replacement.

    Immersion element, Heating coil, Insulation jacket

Then one of two outcomes

Repair

The fault is a part, such as an element, a thermostat or a valve, and the cylinder itself is sound.

Replace

The cylinder itself has failed, for example by leaking from its shell, or repair would not be the sensible route.

What each fixed price includes

Diagnosis, the annual service, replacement labour and a new installation each have one price. The cylinder is priced separately: it depends on type, size and your preference, and we recommend the right one for your home.

Fig. 2Stratified cylinder, sectionNot to scale
Cylinder troubleshooting and diagnosis
No call-out fee.
£180Fixed price
Annual cylinder service
£180Fixed price
Cylinder replacement, labour
Labour and miscellaneous parts. Cylinder priced separately.
£1,450Plus cylinder
New cylinder installation
Pipework, installation, commissioning and Building Regulations. Cylinder priced separately.
£2,400Plus cylinder

No VAT is charged

There is no call-out fee

Cylinder price depends on type, size and your preference; we recommend the right one.

See what each price covers

The parts a diagnosis reaches

Each part is drawn in section. Where a guide to it is published, the plate opens it.

  1. 01TPRV
  2. 02Inlet group
  3. 03Tundish
  4. 04Expansion vessel
  5. 05Immersion element
  6. 06Cylinder thermostat
  7. 07High-limit cut-out
  8. 082-port valve
  9. 09Heating coil
  10. 10Insulation jacket
  11. 11Discharge pipe
  12. 12Airing cupboard
  13. 13Scaled element
  14. 14Failed element
Fig. 3Vented cylinder, sectionNot to scale

Follow the water through the cylinder

Each topic follows the water through the cylinder, from the cold inlet to the hot outlet, and ends in a guide or a fixed-price service.

All guides

One subject, done in the same order every time

London Cylinder Specialist works on hot water cylinders, vented and unvented, and on the valves, vessels, elements and controls around them.

Every cylinder is checked in the same order, and the price of each job is published.

Cover
London inside the M25, 24/7
Prices
Fixed and published. No VAT is charged.
Method
Diagnosis first, in a fixed order.

London Cylinder Specialist is a trading name of London Leak Specialist Ltd, registered in England and Wales, company number 17437507, 71-75 Shelton Street, Covent Garden, London WC2H 9JQ.

Fig. 4A cylinder in its airing cupboard, with room to reach the valves and controls.

Hot water cylinder questions

Plain answers on vented and unvented cylinders, faults and what the work costs.

What is the difference between a vented and an unvented cylinder?

A vented cylinder is fed from a cold water tank, usually in the loft, so its pressure depends on how high that tank sits. An unvented cylinder is fed straight from the mains and supplies hot water at mains pressure. Because the water is sealed in and heats up under pressure, it carries an expansion vessel and safety valves that a vented cylinder does not need.

Why is there no hot water when the heating works?

Heating and hot water are separate circuits that share a heat source. When the radiators warm up but the cylinder does not, the usual suspects are the cylinder thermostat, a motorised valve on the hot water circuit, a failed immersion heater or a fault with the coil. A diagnosis separates them in a fixed order instead of guessing.

Should I repair or replace a hot water cylinder?

That depends on what the diagnosis finds. A failed heater, thermostat or valve on a sound cylinder is a repair. A cylinder that leaks from its own shell cannot sensibly be repaired and needs replacing. The point of diagnosing first is that the decision rests on the fault, not on a sales target.

How much does a hot water cylinder diagnosis cost?

Cylinder troubleshooting and diagnosis is a fixed price of £180. There is no call-out fee, and No VAT is charged. The annual cylinder service is also £180.

Is the cylinder included in the replacement price?

No. A cylinder replacement is a fixed price of £1,450 for labour and miscellaneous parts, and a new cylinder installation is a fixed price of £2,400 that includes pipework, installation, commissioning and Building Regulations. The cylinder itself is priced separately: it depends on type, size and your preference, and we recommend the right one for your home. No VAT is charged.

Is a dripping relief valve or tundish an emergency?

A drip means the unvented cylinder is releasing pressure or heat, and the cause needs finding: it can be the valve, the expansion vessel or the incoming pressure. Steam or very hot water from the discharge pipe is different. Turn off the heat source, keep clear and call an engineer.

What should I tell you when I get in touch?

A phone number and the postcode of the property are enough to start. It helps to add what the cylinder is doing, when it started, and whether it is vented or unvented if you know. Send them through the enquiry form.

Not sure what the cylinder needs?

Describe what it is doing. Diagnosis comes first, then repair or replacement.

Diagnosis
£180 fixed. There is no call-out fee.
Cover
London inside the M25, 24/7
Cylinder
Priced separately. It depends on type, size and your preference, and we recommend the right one.
Hot water cylindersLondon inside the M25, 24/7
Ask about your cylinder